Effects of abdominal and thoracic breathing on breathing pattern components in normal subjects and in patients with chronic obstructive pulmonary disease.

The purpose of this study was to assess the effect of voluntarily controlled breathing maneuvers on breathing pattern components measured noninvasively with the respiratory inductive plethysmograph. In normal subjects, these maneuvers included predominantly thoracic and abdominal patterns with and without visual reinforcement from video-displayed plots of rib cage versus abdominal loops. In patients with chronic obstructive pulmonary disease (COPD), only predominantly abdominal breathing without and with visual feedback was employed; the latter produced greater abdominal contribution to tidal volume. Voluntarily controlled breathing patterns led to increased minute ventilation (VI) in normal subjects because of variable changes of frequency and tidal volume. This increase in ventilation was achieved despite increased asynchronous and paradoxic motion between rib cage and abdominal excursions that would add to the work of breathing. Patients with COPD had heightened baseline respiratory center drive when compared with that in normal subjects, as evidenced by elevation of VI and mean respiratory flow (VT/TI). In contrast to normal subjects, abdominal breathing produced no change in VI and VT/TI for the group as a whole, but 6 of the 9 patients with COPD had decreases compared with natural breathing. This diminution of respiratory drive in some patients with COPD during voluntary abdominal breathing might relate to limitation of ventilatory response by the increased work of breathing caused by pulmonary hyperinflation, elevated airway resistance, and increased asynchronous and paradoxic motion of the rib cage to the abdominal excursions, and/or the mental activity required to perform the breathing maneuver might be inhibitory to respiratory drive.